The use of turbochargers to increase the air intake of internal combustion engines is known to increase engine output. In many conventional turbochargers a compressor wheel is driven at high speeds or revolutions per minute. For example, many compressor wheels rotate in the range of about 100,000 to 150,000 revolutions per minute.
To further accommodate these high speeds, many manufacturers fabricate compressor wheels using lightweight materials such as aluminum and aluminum alloys. The lighter weight materials allow the compressor wheels to have lower rotational inertia. These compressor wheels respond more rapidly to transient conditions of the internal combustion engine. Furthermore, manufacturers typically cast compressor wheels to maintain low cost and reproducibility of complex structures of the compressor wheel.
However, the high speeds have reduced compressor wheel life. Many compressor wheels are attached to a turbine wheel by a shaft. The shaft passes through a bore in the hub of the compressor wheel. A nut or threaded shaft holds the shaft in contact with the hub of the compressor wheel. At higher rotational speeds, centripetal acceleration of the compressor wheel mass creates high tensile loading of the compressor wheel near the bore. This loading is especially severe during transient conditions of the internal combustion engine. The casting process of the compressor wheel creates additional areas for imperfections such as dross, voids, and inclusions where fatigue failure may occur.
In U.S. Pat. No. 4,705,463, issued to Fidel M. Joco on Nov. 10, 1986 the bore of the compressor wheel is nearly eliminated. Instead, the shaft threads into a counter bore. Using the counter bore reduces the stress risers present due to the bore and process of casting such bore. The compressor wheel of this invention has a longer life. However, alignment of the shaft with the wheel, assembly, and servicing of compressors using this invention may be more difficult and expensive.
The present invention is directed to overcoming one or more of the problems as set forth above.